The broad goals of this project are to understand the control of enzyme formation in the arginine biosynthetic pathway of E. coli. During 1978-79, we have continued our studies on the regulatory gene for arginine biosynthesis, arg R. A plasmid carrying the arg R gene was constructed and mapped with a variety of restriction endonucleases. The arg R gene was localized within a 1200 base pair DNA fragment. A method was developed to select for insertion of DNA segments into the arg R gene. With the information we now have, we are in a position to sequence this gene. We have also found that the activity of this gene is regulated by its own product, the arg R repressor protein. This was demonstrated by inserting lactose genes into arg R showing that Beta-galactosidase formation is inhibited in the presence of arginine repressor and the co-repressor, L-arginine. We now plan to isolate mutants in which autoregulation is abolished and which therefore produce more repressor. Such mutants will be useful for the chemical characterization of the repressor protein and for studies on the control of enzyme synthesis in cell-free extracts.